Molding machines for molding multiple items simultaneously are well known. U.S. Pat. No. 4,545,952 to the present inventor shows a typical machine of this type. Other U.S. patents held by the present inventor which are also in the field of this invention include U.S. Pat. Nos. 4,402,657, 4,402,661, 4,550,006, and 4,436,496.
All of the known machines in this field have utility, but they suffer from a common drawback: the multiple cavities are fed with liquid silicone rubber from a common manifold. Thus, no cavity receives individual attention, so to speak. The volume of silicone introduced into each cavity is the same, as is the speed of silicone flow into each cavity and the pressure at which the injection is made.
The process of injecting liquid silicone rubber into the separate cavities at the same volume, speed, pressure and temperature usually results in product of differing quality.
This is because no two cavities in a multi-cavity mold are exactly alike, due to the physical limitations encountered in making machined parts. Even very slight structural variances between cavities can cause differences in flow rates from cavity to cavity, different air venting characteristics, different heat distribution, and so on.
Moreover, as the number of cavities increases, the total length of the runners increases, i.e., the distance the material must travel before entering a cavity increases. Thus, the material heats up and begins to cure as it travels toward the cavities. To avoid premature curing, it becomes necessary to speed up the flow rate of the material through the runners, to cool the mold, or both. Rapid injection creates pressure drops in the runners, requiring a higher injection pressure and such higher pressure creates still further problems. Thus, the solution to each problem creates still further problems that require further countermeasures, and so on. In short, complexity leads to more complexity and as more parameters require controlling, the goal of perfection continually eludes the designer. As the number of cavities and hence the length of the runners increases, the range of practical temperatures, pressures, injection rates and the like are narrowed and the task of producing identical high quality parts becomes increasingly difficult.
Accordingly, most inventors have worked tirelessly to refine the existing molding machines. They have devised better runners, better ways of making the initial mixture more homogenous, better means for cooling molds, for controlling injection pressures, and the like. These refinements have led to better and better product, at higher and higher costs.
The conventional wisdom in the industry is that most of the developments in this field are in the past, and that the future holds nothing but continued relatively minor refinements. Thus, nothing in the art suggests that an entirely new, revolutionary approach is possible. On the contrary, every indication is that pioneering breakthroughs will not occur in this field.